Sodium channels play a diverse set of roles in maintaining normal and pathological states, including the long recognized role that voltage gated sodium channels play in the generation of abnormal neuronal activity and neuropathic or pathological pain. Damage to peripheral nerves following trauma or disease can result in changes to sodium channel activity and the development of abnormal afferent activity including ectopic discharges from axotomised afferents and spontaneous activity of sensitized intact nociceptors. These changes can produce long-lasting abnormal hypersensitivity to normally innocuous stimuli, or allodynia. Examples of neuropathic pain include, but are not limited to, post-herpetic neuralgia, trigeminal neuralgia, diabetic neuropathy, chronic lower back pain, phantom limb pain, and pain resulting from cancer and chemotherapy, chronic pelvic pain, complex regional pain syndrome and related neuralgias.
There have been some advances in treating neuropathic pain symptoms by using medications, such as gabapentin, and more recently pregabalin, as short-term, first-line treatments. However, pharmacotherapy for neuropathic pain has generally had limited success with little response to commonly used pain reducing drugs, such as NSAIDS and opiates. Consequently, there is still a considerable need to explore novel treatment modalities.
There remain a limited number of potent effective sodium channel blockers with a minimum of adverse events in the clinic. There is also an unmet medical need to treat neuropathic pain and other sodium channel associated pathological states effectively and without adverse side effects.
PCT Published Patent Application No. WO 2006/110917, PCT Published Patent Application No. WO 2010/45251 and PCT Patent Application No. PCT/US2010/040187 discloses certain spiro-oxindole compounds. These compounds are disclosed therein as being useful for the treatment of sodium channel-mediated diseases, preferably diseases related to pain, central nervous conditions such as epilepsy, anxiety, depression and bipolar disease; cardiovascular conditions such as arrhythmias, atrial fibrillation and ventricular fibrillation; neuromuscular conditions such as restless leg syndrome; neuroprotection against stroke, neural trauma and multiple sclerosis; and channelopathies such as erythromelalgia and familial rectal pain syndrome.
Methods of preparing these compounds and pharmaceutical compositions containing them are also disclosed in PCT Published Patent Application No. WO 2006/110917, PCT Published Patent Application No. WO 2010/45251 and PCT Patent Application No. PCT/US2010/040187.
There exists, therefore, a need for improved methods of preparing certain spiro-oxindole compounds.